Plants have totipotency, such that they are able to form calluses from somatic cells that have been highly differentiated. If calluses are cultured under constant conditions, also, plant bodies can be reproduced through differentiation of adventitious embryos, adventitious buds, and adventitious roots. Callus culture is advantageous in the following respect; for example, 1) it has reproductive integrity; 2) it has the ability to differentiate a callus cell mass into various tissues and individuals; 3) a large quantity of homogeneous growth cells that are difficult to obtain in plants can be obtained; 4) a callus is suitable as an experimental material because of the absence of seasonal changes in the quality or quantity of cells; 5) the influence of a substance that has been added to the medium on plants can be directly observed; and 6) some plant species are easily induced to undergo genetic variation as a result of callus formation, and such plants can be used for breeding. Thus, callus culture has been extensively used for the production of useful materials, the development of new varieties, the gene introduction into plants, the reproduction of transformants, the production of artificial seeds, and other purposes.
In general, a callus is produced by a method in which a piece of plant tissue is cultured in a medium containing phytohormones (i.e., auxin and cytokinine) (Skoog, F., and Miller, C. O., 1957, Chemical regulation of growth and organ formation in plant tissue cultured in vitro, Symp. Soc. Exp. Biol., 54, 118-130). This method was established over 30 years ago, and this technique is indispensable for the production of transgenic crops at present. However, types of auxin and cytokinine to be used and the amount of auxin relative to that of cytokinine vary depending on plant species. Accordingly, it has been difficult to find adequate conditions for callus formation.
As synthetic auxins, 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxy acetic acid are known, and, concerning an analog thereof; i.e., 4-chlorophenoxyacetic acid, it was reported that the number of days required for leaf tissue culture of African violet, from implanting of explants to callus formation, and formation of adventitious shoots and adventitious roots, was reduced as a result of treatment performed at a particular concentration (Miyoshi Hakozaki et al., Effects of 4-Chlorophenoxyacetic Acid on the Callus and Adventitious Organogenesis from Cultured Leaf Explant African Violet in Vitro, Memoirs of the Institute of Science and Technology, Meiji University, 40, 1-7, 2001). However, callus formation efficiency was not high, and plant species capable of callus formation were limited.
As a 1,4-disubstituted piperazine derivative, JP H6-67668 (B) (1994) describes that N-methyl-N′-phenylacetylpiperazine, N-benzyl-N′-benzoylpiperazine, and the like are useful as decolorants against the color development system of bicolor thermal recording materials.
JP 2002-503239 (A) describes that a piperazine derivative having substituents at positions other than 1- and 4-positions of the piperazine ring is useful as an anti-inflammatory agent.
Fipexide, which is a type of a 1,4-disubstituted piperazine derivative (e.g., 1-[(p-chlorophenoxy)acetyl]-4-piperonylpiperazine or 1-(4-chlorophenoxyacetyl)-4-(1,3-benzodioxole-5-ylmethyl)piperazine), is known as an antidepressant.
Further, 1-piperonylpiperazine (1-(3,4-methylenedioxybenzyl)piperazine) and many 1-substituted piperazine derivatives as analogs thereof are commercially available as raw materials for chemical production.
However, there has been no report demonstrating that 1,4-disubstituted piperazine derivatives and 1-substituted piperazine derivatives are capable of callus induction.